Two types of purification and separation processes involving mixed gas streams containing hydrogen are generally used. In one type of purification process the contaminants are adsorbed and a purified hydrogen stream allowed to pass through the bed. In another type of process, hydrogen is removed via contact with a hydridable material and the contaminants passed through the bed. The following patents with respect to the first type of process are believed pertinent:
Banikotes et al, U.S. Pat. No. 3,839,847, disclose a multi-reactor adiabatic pressure swing cycle for purifying a hydrogen rich (97% or greater) gas stream by absorbing the contaminant gases mixed with hydrogen on an absorbent medium, such as silica gel, molecular sieves, or activated charcoal and allowing the hydrogen in pure form to pass through. Banikotes et al also suggests control of temperature fluctuation within the bed, between adsorption and desorption cycles, to approach isothermal operation by proper combination of the adsorption material, e.g. 6-10 U.S. standard mesh silica gel with a non-adsorbent material, such as particulate (6-10 U.S. Standard mesh) aluminum or other materials such as iron or steel, selected with regard to the heat capacity, heat conductivity and density of the combination.
Hoke et al, U.S. Pat. No. 3,141,748, disclose a process for recovering pure hydrogen from a vapor stream comprising hydrogen and a mixture of hydrocarbon compounds. In this process the adsorbent is chosen which has a higher affinity for the hydrocarbon than it has for hydrogen, e.g. activated charcoal or alumina thus permitting the hydrogen to pass through the absorption bed as a relatively pure (99.0+mole percent hydrogen) stream. A two-stage depressurization stage process is used.
The second type of hydrogen purification process utilizes a hydridable material, and such material combines chemically with hydrogen to form metallic hydrides. Thus, in contrast to the processes described above, hydrogen is the component adsorbed and the contaminants are allowed to pass through. The following patents relate to hydrogen separation or storage and storage processes using a hydridable material:
Reilly et al, U.S. Pat. No. 3,793,435 discloses a process for separating hydrogen from other gaseous products such as O.sub.2, N.sub.2, CO, CO.sub.2, H.sub.2 O and CH.sub.4. Separation is achieved by contacting the gas mixture with a distributed form of an alloy of a rare earth lanthanum and nickel in an active state, the metal forming a hydride on contact with the hydrogen. Hydrogen separation is effected by passing a gas mixture at an initial pressure of 175 psia through a tubular reactor containing an inert, high porosity packing to prevent agglomeration at room temperature removing an effluent gas at a pressure of 116-133 psia and then desorbing by reducing the pressure to 25 psia.
Blytas, U.S. Pat. No. 4,036,944 discloses an isothermal process for recovering hydrogen from gas mixtures and waste gas streams, particularly from refinery sources using a hydrogen solvent. The hydrogen sorbent comprises a hydridable material, e.g., an alloy of lanthanum pentanickel and a polymeric binder. Optionally, the sorbent contains inert components such as copper, nickel or iron. Such components are alleged as useful for heat sinks and heat moderators in the adsorption process. The specific polymeric binder matrix improves the attrition resistance of the hydrogen sorbent, and such binders include block copolymers of polystyrene-polybutadiene and polyisoprene-polystyrene. The examples show utilizing a fixed bed reactor containing reactor tubes loaded with pellets of the sorbent-binder with a jacket around the reactor for passage of cooling water to maintain isothermal conditions. Pellets of lanthanum nickel powder with 15% water glass as well as lanthanum nickel-copper powder mixtures (copper powder addition up to 50% by weight) without the polymeric binder were used to reduce expansion. The resulting phases upon hydrogenation expanded over 4%, and after two cycles of hydrogenation, they disintegrated.
Woolley, U.S. Pat. No. 4,185,979 discloses a process for transferring heat to or from metal hydrides contained in a storage container. In the prior art, tubes were spaced throughout the bed of hydride material and a heat exchange material was circulated outside these tubes to heat or cool the reactor as required. Other processes have used the gas itself as a means of forming or cooling gas streams for absorption or desorption as required.
Billings, U.S. Pat. No. 4,108,605 discloses a process for treating a mixture of hydrogen and impurity gases by passing the gas to a hydride container where the hydrogen is absorbed by the hydride forming material. To facilitate absorption and release of the hydrogen and impurities from the hydride forming material, a cooling fluid pump and heat exchanger and a heating fluid pump and heat exchanger are provided.
Sandrock et al, in U.S. Pat. Nos. 4,079,523; 4,096,639; 4,096,641 and 4,079,523; disclose various hydridable alloys which are suited for recovering hydrogen from a gas stream.
Turillon et al, in U.S. Pat. Nos. 4,135,621; 4,134,490; 4,134,491 and 4,133,426 disclose the use of specially extended particles of solid having low apparent density distributed within a mass of metal hydride as a system for storing hydrogen. Mixtures of hydridable metal and particulate solids, i.e., metal powders such as nickel powder are added to the hydrogen storage vessel. Also disclosed are the use of dry diatomaceous earth, lignin, metal whiskers, the powder combined to provide a packing density of not greater than 30% of the theoretical density of the powder itself. The '491 patent discloses the use of collapsible structures.
In another document, Sandrock et al disclose an adiabatic process which uses a thermal ballast with a hydride storage material to recover the energy generated during exothermic hydriding, that energy stored in the thermal ballast. The examples show using a bath of water or molten sodium sulfate decahydrate as thermal ballast to recover the heat generated during hydriding and recovering the heat from the bath to enhance desorption.